Stop washers of the pre-cited type with the most different of configurations are already known. They serve as an axial stop for the planet gear and protect the unhardened planet gear carrier as well as the planet gear from wear. The planet gear runs with a flat end face against a likewise flat stop surface of the stop washer. The planet gear comprises a through-bore with which it is mounted with the help of a bearing for rotation on the planet gear axle. This bearing can be constituted, for example, by a needle roller crown ring or even by a full complement needle roller set. Depending on the type of bearing, therefore, either the bearing cage or the ends of the bearing needles run on the stop washers. The stop washers are generally punched out of sheet metal. The surface of the stop washers is either ground or left in as-rolled state, or coated. The choice of the material of the washers and their surface quality and hardness depends essentially on the friction conditions prevailing.
Very often, however, the lubrication conditions at the points of contact between the stop washers and the end faces of the planet gears are unsatisfactory. In this case, bronze washers are also used as stop washers. Now and then, even two stop washers of different materials are inserted next to each other or multi-layer stop washers, for instance, plated sheet metal washers combining steel and bronze are used. This arrangement takes into account the different contact and friction conditions between the planet gear and the stop washer and between the stop washer and the planet gear carrier.
A positive influence is also exerted on the lubricant circulation within the planetary transmission and particularly at the bearing arrangement for the planet gear by an appropriate configuration of the stop washers. The lubricant circulation in the bearing arrangement of the planet gear and the lubrication of the stop surfaces of the stop washers in the region of contact with the planet gear is achieved by a purposed provision of oil grooves in the surface of the stop washers or also with axial openings.
A stop washer of this type is known, for example, from DE 35 02 076 C1. This stop washer has two flat end faces configured as stop surfaces and comprises an angular opening through which lubricant is conveyed to the bearing. Another stop washer known from DE 198 04 734 A1 is configured as a flat steel ring whose end faces are embossed and whose reception bore comprises openings. Stop washers of the pre-cited type are also disclosed in DE 44 18 693 C1.
A drawback of these stop washers is that when the planet gear runs axially against the stop washer under unfavorable conditions, the lubricant film can be torn off or interrupted at the points of contact. This results in deficient lubrication and premature wear at the points of contact and, in the extreme case, in a failure of the entire planetary transmission.